In addition to a reduction in the fuel consumption, direct-injection diesel engines must meet the requirement of a reduction in emissions. For this, it is very important to provide the longest possible, clear injection distance for the diesel fuel jet and to avoid, if possible, any fuel hitting the cylinder walls, so as to obtain the most uniform fuel-air-mixture.
For a proper processing of the mixture, European Patent A-0 634 572, for example, discloses that given an essentially level limiting surface of the combustion chamber near the cylinder head, the admission channels must be installed such that the air flowing into the cylinder will be provided with a strong rotational movement around the cylinder axis, which is still in effective during the injection of fuel. However, this can be achieved only with a geometrically complicated cylinder head.
German Patent A-4 241 104 discloses a diesel engine, for which the combustion chamber of the cylinder is offset, meaning it has two stages on the cylinder head side that are height-displaced relative to each other. In that case, the admission valve opens up into the surface of the upper stage and the discharge valve issues from the lower stage surface, respectively with the associated channels for conducting gas. The piston bottom has a corresponding design with stages. The respective transition region from one stage to the other is provided at the cylinder head as well as at the piston bottom with an undercut, so that an essentially cylindrical combustion chamber space forms if the piston is in the upper dead center position, which extends crosswise to the cylinder axis. The injector discharges in axial direction of the combustion chamber into this combustion chamber space, that is to say crosswise to the cylinder axis. This structural design also requires a complicated design for the cylinder head and a complicated piston design.
German Patent A-19 537 028 discloses a diesel engine that is modified relative to German Patent A-4 241 104. The admission valves for this engine are again arranged higher than the discharge valves, but the limiting surface of the combustion chamber on the cylinder-head side is slanted on the intake side, as compared to the cylinder axis, and extends horizontally on the discharge side. The associated piston bottom has a corresponding outline, wherein the essentially horizontal piston bottom surface that is coordinated with the discharge side extends into the intake region. Thus, a cylindrical combustion chamber space is created in the upper dead center position, which extends crosswise to the cylinder axis and into which fuel is injected crosswise to the cylinder axis. This combustion chamber design also requires geometrically complicated cylinder heads and pistons with a fissured piston bottom design.
Thus, it is the object of the invention to create a direct-injection diesel engine, effecting a diesel combustion method that permits high center pressures with a very favorable fuel consumption and low emissions, owing to its combustion chamber design.
This object is solved with a diesel engine having individual cylinders that are respectively provided with a fuel injection device, for which the injector discharges into the combustion chamber of the cylinder, said cylinders having at least one discharge valve and at least one admission valve for each cylinder, to which are assigned respectively extending channels in the cylinder head. These channels empty at a slant into the combustion chamber, wherein the combustion chamber is limited by the cylinder head on one side and the piston bottom on the other side and is designed such that the charge movement inside the combustion chamber is a rotational movement around the cylinder axis, with a value of CU/CAxe2x89xa60.5 and a tumble movement around the lateral axis with a value of CT/CAxe2x89xa70.5, wherein the injector is provided with at least one injection opening. CU refers to the circumferential speed component for a rotational flow and CA correspondingly refers to the axial speed component, so that the ratio CU/CA represents a measure for the intensity of a rotational flow. Analogous to the rotational flow, CT provides the tangential speed component of the tumble or roll turbulence, whereas CA reflects the axial speed component. The ratio CT/CA represents the measure for the intensity of the tumble flow. The device described in German Patent A-41 33 277, for example, can be used for measuring the tumble flow.
By designing the combustion chamber in this way, together with a separation of the fuel to be injected into a plurality of individual jets, it is possible to produce an optimum mixture inside the combustion chamber, resulting for the most part in a homogeneous fuel-air-mixture. It is particularly useful in this connection if the fuel is injected into the combustion chamber with an extremely high pressure, such as can be realized with the aid of so-called common-rail injection systems and pressures exceeding 1000 bar. In particular the intake configuration is embodied with two essentially parallel extending admission channels that discharge at a slant into the combustion chamber, so that the homogeneous mixture for a direct-injection diesel engine is achieved through a so-called tumble movement. The combustion chamber limiting surface on the cylinder head side can have a level design, at least in part, such as is known from classic diesel engine designs. The achieved, induced center pressures are in the range of 12 to 14 bar for a rotational speed of 1500 RPM, for example, and in the range of 15 to 18 bar for 2000 RPM, as well as in the range of 10 to 13 bar for 4000 RPM.
One embodiment of the invention provides that the combustion chamber limiting surface on the cylinder-head side has a roof-shaped design, at least in its essential region, wherein at least one admission channel feeds into one roof surface and at least one discharge channel issues from the other roof surface. It is particularly favorable in this case if the roof-shaped limiting region is respectively level in the area adjacent to the xe2x80x9ceaves regionxe2x80x9d of the roof. The piston bottom is designed to match the combustion chamber limiting surface on the cylinder-head side. It has turned out that this combustion chamber design, which is derived from Otto engines and adapted to the diesel method, also results in excellent values for the diesel method with respect to output, fuel consumption and low emissions, provided the aforementioned conditions of CU/CAxe2x89xa60.5 and CT/CAxe2x89xa70.5 are observed for the charge movement.
One advantageous embodiment of the invention furthermore provides that the piston bottom contains an indentation, preferably a pot-shaped indentation. For this, it is useful if the indentation has an essentially circular-cylindrical shape and a level bottom surface. With a partially roof-shaped piston bottom design, the indentation is arranged in the region of the cylinder axis, so that only the remaining outer edge regions have a roof-shaped design. A level limiting surface toward the cylinder wall is provided adjacent to the xe2x80x9ceaves regionxe2x80x9d of the roof, in accordance with the outline of the limiting surface on the cylinder head side.
One advantageous embodiment of the invention provides that the vertical axis of the indentation coincides with the vertical axis of the injection device, wherein it is particularly advantageous that the vertical axis of the injection device is arranged at a distance and offset in the direction of the discharge valve.
The invention is explained in further detail with the aid of schematic drawings of exemplary embodiments, showing in:
FIG. 1 a vertical section through a cylinder;
FIG. 2 a vertical section through the upper region of a piston, along the cylinder axis;
FIG. 3 an associated view from above of the piston according to FIG. 2;
FIG. 4 a rotational flow that has formed at the end of the intake phase;
FIG. 5 a tumble flow that has formed;
FIG. 6 schematically the development of a tumble flow in the intake phase;
FIG. 7 the arrangement of injector openings for an injector;
FIG. 8 a modified arrangement for the injector openings;
FIG. 9 an arrangement of injector openings where the openings are at different distances to each other.